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IGO 2021 A1

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Acute-angled triangle ABCABC with circumcircle ω\omega is given. Let DD be the midpoint of ACAC , EE be the foot of altitude from AA to BCBC , and FF be the intersection point of ABAB and DEDE . Point HH lies on the arc BCBC of ω\omega (the one that does not contain AA ) such that ∠BHE=∠ABC\angle BHE=\angle ABC . Prove that ∠BHF=90∘\angle BHF=90^\circ .

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